The ball-lock type connector having a mechanism of locking a connector and a counterpart connector in a connected state is already known (Patent Literature 1 and Patent Literature 2, for example).
The connector of this type is configured such that it includes an engaging ball (lock ball) accommodated movably in a diameter direction in a ball support hole of a cylindrical fitting part of the connector. When part of the engaging ball projecting from a circumferential surface of the cylindrical fitting part becomes engaged with an engaging groove of a counterpart connector fitting to the cylindrical fitting part, the connectors are held in a connected state with each other.